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Old CM (4228a/4248a/3023) Hardware Hacks

58K views 293 replies 19 participants last post by  lenlab 
#1 ·
Here are the CM4248a / CM3023 graphs on the unmodified, as from the factory, antenna:


Raw Gain:


SWR:


NEC file:
Code:
CM CM4248 :  Channel Master 4248, converted with 4nec2 on 10-Jul-08 2:25
CM AGT = 1.0 (0 db) at 585 mhz.  Autosegmentation = 21
CE
GW	8	1	7.2	1.125	-0.8	7.35	1.4	-0.8	0.05
GW	9	1	7.35	1.4	-0.8	7.45	1.7	-0.8	0.05
GW	10	3	7.45	1.7	-0.8	7.45	3.15	-1.07	0.05
GW	11	3	7.45	3.15	-1.07	7.45	4.6	-1.33	0.05
GW	12	3	7.45	4.6	-1.33	7.45	5.25	0	0.05
GW	13	3	7.45	5.25	0	7.45	4.6	1.33	0.05
GW	14	3	7.45	4.6	1.33	7.45	3.15	1.07	0.05
GW	15	3	7.45	3.15	1.07	7.45	1.7	0.8	0.05
GW	16	3	7.45	1.7	0.8	7.45	0.88	0.8	0.05
GW	17	1	7.45	0.88	0.8	7.45	0.38	0.8	0.05
GW	18	1	7.2	1.125	-0.8	7.05	1.4	-0.8	0.05
GW	19	1	7.05	1.4	-0.8	6.95	1.7	-0.8	0.05
GW	20	3	6.95	1.7	-0.8	6.95	3.15	-1.07	0.05
GW	21	3	6.95	3.15	-1.07	6.95	4.6	-1.33	0.05
GW	22	3	6.95	4.6	-1.33	6.95	5.25	0	0.05
GW	23	3	6.95	5.25	0	6.95	4.6	1.33	0.05
GW	24	3	6.95	4.6	1.33	6.95	3.15	1.07	0.05
GW	25	3	6.95	3.15	1.07	6.95	1.7	0.8	0.05
GW	26	3	6.95	1.7	0.8	6.95	0.88	0.8	0.05
GW	27	1	6.95	0.88	0.8	6.95	0.38	0.8	0.05
GW	28	1	7.45	1.7	-0.8	6.95	1.7	-0.8	0.05
GW	29	1	7.45	3.15	-1.07	6.95	3.15	-1.07	0.05
GW	30	1	7.45	4.6	-1.33	6.95	4.6	-1.33	0.05
GW	31	1	7.45	5.25	0	6.95	5.25	0	0.05
GW	32	1	7.45	4.6	1.33	6.95	4.6	1.33	0.05
GW	33	1	7.45	3.15	1.07	6.95	3.15	1.07	0.05
GW	34	1	7.45	1.7	0.8	6.95	1.7	0.8	0.05
GW	35	1	7.45	0.88	0.8	6.95	0.88	0.8	0.05
GW	36	1	7.45	0.38	0.8	6.95	0.38	0.8	0.05
GW	37	1	6.95	0.88	0.8	6.25	0.88	0.8	0.05
GW	38	3	6.95	0.38	0.8	5.95	0.38	0.8	0.05
GW	39	1	5.95	0.38	0.8	5.95	0.58	0.8	0.05
GW	40	1	5.95	0.58	0.8	6.25	0.88	0.8	0.05
GW	41	5	5.95	0.38	0.8	4.2	0.38	0.8	0.05
GW	42	5	5.95	0.58	0.8	4.2	0.58	0.8	0.025
GW	43	1	4.2	0.38	0.8	4.2	0.58	0.8	0.025
GW	44	3	4.2	0.38	0.8	2.95	0.38	0.8	0.025
GW	45	3	4.2	0.58	0.8	2.95	0.58	0.8	0.025
GW	46	1	7.2	-1.125	-0.8	7.35	-1.4	-0.8	0.05
GW	47	1	7.35	-1.4	-0.8	7.45	-1.7	-0.8	0.05
GW	48	3	7.45	-1.7	-0.8	7.45	-3.15	-1.07	0.05
GW	49	3	7.45	-3.15	-1.07	7.45	-4.6	-1.33	0.05
GW	50	3	7.45	-4.6	-1.33	7.45	-5.25	0	0.05
GW	51	3	7.45	-5.25	0	7.45	-4.6	1.33	0.05
GW	52	3	7.45	-4.6	1.33	7.45	-3.15	1.07	0.05
GW	53	3	7.45	-3.15	1.07	7.45	-1.7	0.8	0.05
GW	54	3	7.45	-1.7	0.8	7.45	-0.88	0.8	0.05
GW	55	1	7.45	-0.88	0.8	7.45	-0.38	0.8	0.05
GW	56	1	7.2	-1.125	-0.8	7.05	-1.4	-0.8	0.05
GW	57	1	7.05	-1.4	-0.8	6.95	-1.7	-0.8	0.05
GW	58	3	6.95	-1.7	-0.8	6.95	-3.15	-1.07	0.05
GW	59	3	6.95	-3.15	-1.07	6.95	-4.6	-1.33	0.05
GW	60	3	6.95	-4.6	-1.33	6.95	-5.25	0	0.05
GW	61	3	6.95	-5.25	0	6.95	-4.6	1.33	0.05
GW	62	3	6.95	-4.6	1.33	6.95	-3.15	1.07	0.05
GW	63	3	6.95	-3.15	1.07	6.95	-1.7	0.8	0.05
GW	64	3	6.95	-1.7	0.8	6.95	-0.88	0.8	0.05
GW	65	1	6.95	-0.88	0.8	6.95	-0.38	0.8	0.05
GW	66	1	7.45	-1.7	-0.8	6.95	-1.7	-0.8	0.05
GW	67	1	7.45	-3.15	-1.07	6.95	-3.15	-1.07	0.05
GW	68	1	7.45	-4.6	-1.33	6.95	-4.6	-1.33	0.05
GW	69	1	7.45	-5.25	0	6.95	-5.25	0	0.05
GW	70	1	7.45	-4.6	1.33	6.95	-4.6	1.33	0.05
GW	71	1	7.45	-3.15	1.07	6.95	-3.15	1.07	0.05
GW	72	1	7.45	-1.7	0.8	6.95	-1.7	0.8	0.05
GW	73	1	7.45	-0.88	0.8	6.95	-0.88	0.8	0.05
GW	74	1	7.45	-0.38	0.8	6.95	-0.38	0.8	0.05
GW	75	1	6.95	-0.88	0.8	6.25	-0.88	0.8	0.05
GW	76	3	6.95	-0.38	0.8	5.95	-0.38	0.8	0.05
GW	77	1	5.95	-0.38	0.8	5.95	-0.58	0.8	0.05
GW	78	1	5.95	-0.58	0.8	6.25	-0.88	0.8	0.05
GW	79	5	5.95	-0.38	0.8	4.2	-0.38	0.8	0.05
GW	80	5	5.95	-0.58	0.8	4.2	-0.58	0.8	0.025
GW	81	1	4.2	-0.38	0.8	4.2	-0.58	0.8	0.025
GW	82	3	4.2	-0.38	0.8	2.95	-0.38	0.8	0.025
GW	83	3	4.2	-0.58	0.8	2.95	-0.58	0.8	0.025
GW	84	69	1.49	16.65	1.94	1.49	-16.65	1.94	0.125
GW	85	69	3.35	16.65	4.36	3.35	-16.65	4.36	0.125
GW	86	69	5.21	16.65	6.77	5.21	-16.65	6.77	0.125
GW	87	69	7.07	16.65	9.19	7.07	-16.65	9.19	0.125
GW	88	69	9.81	16.65	12.75	9.81	-16.65	12.75	0.125
GW	89	69	12.55	16.65	16.32	12.55	-16.65	16.32	0.125
GW	90	69	15.29	16.65	19.87	15.29	-16.65	19.87	0.125
GW	91	69	1.49	16.65	-1.94	1.49	-16.65	-1.94	0.125
GW	92	69	3.35	16.65	-4.36	3.35	-16.65	-4.36	0.125
GW	93	69	5.21	16.65	-6.77	5.21	-16.65	-6.77	0.125
GW	94	69	7.07	16.65	-9.19	7.07	-16.65	-9.19	0.125
GW	95	69	9.81	16.65	-12.75	9.81	-16.65	-12.75	0.125
GW	96	69	12.55	16.65	-16.32	12.55	-16.65	-16.32	0.125
GW	97	69	15.29	16.65	-19.87	15.29	-16.65	-19.87	0.125
GW	98	13	12.47	2.86	0	12.47	-2.86	0	0.035
GW	99	13	18.04	2.86	0	18.04	-2.86	0	0.035
GW	100	13	23.61	2.86	0	23.61	-2.86	0	0.035
GW	101	13	29.18	2.86	0	29.18	-2.86	0	0.035
GW	102	13	34.75	2.86	0	34.75	-2.86	0	0.035
GW	103	13	40.32	2.86	0	40.32	-2.86	0	0.035
GW	104	13	45.89	2.86	0	45.89	-2.86	0	0.035
GW	105	13	51.46	2.86	0	51.46	-2.86	0	0.035
GW	106	13	57.03	2.86	0	57.03	-2.86	0	0.035
GW	107	13	62.6	2.86	0	62.6	-2.86	0	0.035
GW	108	13	68.17	2.86	0	68.17	-2.86	0	0.035
GW	109	13	73.74	2.86	0	73.74	-2.86	0	0.035
GW	110	13	79.31	2.86	0	79.31	-2.86	0	0.035
GW	111	13	84.88	2.86	0	84.88	-2.86	0	0.035
GW	112	13	12.87	2.86	0	12.87	-2.86	0	0.035
GW	113	13	18.44	2.86	0	18.44	-2.86	0	0.035
GW	114	13	24.01	2.86	0	24.01	-2.86	0	0.035
GW	115	13	29.58	2.86	0	29.58	-2.86	0	0.035
GW	116	13	35.15	2.86	0	35.15	-2.86	0	0.035
GW	117	13	40.72	2.86	0	40.72	-2.86	0	0.035
GW	118	13	46.29	2.86	0	46.29	-2.86	0	0.035
GW	119	13	51.86	2.86	0	51.86	-2.86	0	0.035
GW	120	13	57.43	2.86	0	57.43	-2.86	0	0.035
GW	121	13	63	2.86	0	63	-2.86	0	0.035
GW	122	13	68.57	2.86	0	68.57	-2.86	0	0.035
GW	123	13	74.14	2.86	0	74.14	-2.86	0	0.035
GW	124	13	79.71	2.86	0	79.71	-2.86	0	0.035
GW	125	13	85.28	2.86	0	85.28	-2.86	0	0.035
GW	126	5	7.2	-1.125	-0.8	7.2	1.125	-0.8	0.0216
GS	0	0	0.0254		' All in in.
GE	0
EK
LD	5	0	0	0	2.5e7	0
EX	0	126	3	0	1	0
GN	-1
FR	0	1	0	0	761	0
 
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#2 ·
The CM-4248a / CM-3023 already has a plenty wide 33.3 inch wide stock corner reflector (more than 2 times the width of the driven element) and a driven element that by itself peaks at 527 mhz (channel 23) Net Gain. So all that needs to be done to improve it for the new UHF TV band is to rescale the directors lengths and spacings. Pretty easy mod, as mods go.
Here are the graphs with the directors rescaled to peak at 641 mhz :

Raw Gain:


SWR:


NEC file:

Code:
CM CM4248 :  Channel Master 4248, converted with 4nec2 on 10-Jul-08 2:25
CM Rescaled the directors only to peak the antenna gain at 641 mhz.
CM AGT = 1.0 (0 db) at 585 mhz.  Autosegmentation = 21
CE
GW	8	1	7.2	1.125	-0.8	7.35	1.4	-0.8	0.05
GW	9	1	7.35	1.4	-0.8	7.45	1.7	-0.8	0.05
GW	10	5	7.45	1.7	-0.8	7.45	3.15	-1.07	0.05
GW	11	5	7.45	3.15	-1.07	7.45	4.6	-1.33	0.05
GW	12	5	7.45	4.6	-1.33	7.45	5.25	0	0.05
GW	13	5	7.45	5.25	0	7.45	4.6	1.33	0.05
GW	14	5	7.45	4.6	1.33	7.45	3.15	1.07	0.05
GW	15	5	7.45	3.15	1.07	7.45	1.7	0.8	0.05
GW	16	3	7.45	1.7	0.8	7.45	0.88	0.8	0.05
GW	17	1	7.45	0.88	0.8	7.45	0.38	0.8	0.05
GW	18	1	7.2	1.125	-0.8	7.05	1.4	-0.8	0.05
GW	19	1	7.05	1.4	-0.8	6.95	1.7	-0.8	0.05
GW	20	5	6.95	1.7	-0.8	6.95	3.15	-1.07	0.05
GW	21	5	6.95	3.15	-1.07	6.95	4.6	-1.33	0.05
GW	22	5	6.95	4.6	-1.33	6.95	5.25	0	0.05
GW	23	5	6.95	5.25	0	6.95	4.6	1.33	0.05
GW	24	5	6.95	4.6	1.33	6.95	3.15	1.07	0.05
GW	25	5	6.95	3.15	1.07	6.95	1.7	0.8	0.05
GW	26	3	6.95	1.7	0.8	6.95	0.88	0.8	0.05
GW	27	1	6.95	0.88	0.8	6.95	0.38	0.8	0.05
GW	28	1	7.45	1.7	-0.8	6.95	1.7	-0.8	0.05
GW	29	1	7.45	3.15	-1.07	6.95	3.15	-1.07	0.05
GW	30	1	7.45	4.6	-1.33	6.95	4.6	-1.33	0.05
GW	31	1	7.45	5.25	0	6.95	5.25	0	0.05
GW	32	1	7.45	4.6	1.33	6.95	4.6	1.33	0.05
GW	33	1	7.45	3.15	1.07	6.95	3.15	1.07	0.05
GW	34	1	7.45	1.7	0.8	6.95	1.7	0.8	0.05
GW	35	1	7.45	0.88	0.8	6.95	0.88	0.8	0.05
GW	36	1	7.45	0.38	0.8	6.95	0.38	0.8	0.05
GW	37	3	6.95	0.88	0.8	6.25	0.88	0.8	0.05
GW	38	3	6.95	0.38	0.8	5.95	0.38	0.8	0.05
GW	39	1	5.95	0.38	0.8	5.95	0.58	0.8	0.05
GW	40	1	5.95	0.58	0.8	6.25	0.88	0.8	0.05
GW	41	5	5.95	0.38	0.8	4.2	0.38	0.8	0.05
GW	42	5	5.95	0.58	0.8	4.2	0.58	0.8	0.025
GW	43	1	4.2	0.38	0.8	4.2	0.58	0.8	0.025
GW	44	3	4.2	0.38	0.8	2.95	0.38	0.8	0.025
GW	45	3	4.2	0.58	0.8	2.95	0.58	0.8	0.025
GW	46	1	7.2	-1.125	-0.8	7.35	-1.4	-0.8	0.05
GW	47	1	7.35	-1.4	-0.8	7.45	-1.7	-0.8	0.05
GW	48	5	7.45	-1.7	-0.8	7.45	-3.15	-1.07	0.05
GW	49	5	7.45	-3.15	-1.07	7.45	-4.6	-1.33	0.05
GW	50	5	7.45	-4.6	-1.33	7.45	-5.25	0	0.05
GW	51	5	7.45	-5.25	0	7.45	-4.6	1.33	0.05
GW	52	5	7.45	-4.6	1.33	7.45	-3.15	1.07	0.05
GW	53	5	7.45	-3.15	1.07	7.45	-1.7	0.8	0.05
GW	54	3	7.45	-1.7	0.8	7.45	-0.88	0.8	0.05
GW	55	1	7.45	-0.88	0.8	7.45	-0.38	0.8	0.05
GW	56	1	7.2	-1.125	-0.8	7.05	-1.4	-0.8	0.05
GW	57	1	7.05	-1.4	-0.8	6.95	-1.7	-0.8	0.05
GW	58	5	6.95	-1.7	-0.8	6.95	-3.15	-1.07	0.05
GW	59	5	6.95	-3.15	-1.07	6.95	-4.6	-1.33	0.05
GW	60	5	6.95	-4.6	-1.33	6.95	-5.25	0	0.05
GW	61	5	6.95	-5.25	0	6.95	-4.6	1.33	0.05
GW	62	5	6.95	-4.6	1.33	6.95	-3.15	1.07	0.05
GW	63	5	6.95	-3.15	1.07	6.95	-1.7	0.8	0.05
GW	64	3	6.95	-1.7	0.8	6.95	-0.88	0.8	0.05
GW	65	1	6.95	-0.88	0.8	6.95	-0.38	0.8	0.05
GW	66	1	7.45	-1.7	-0.8	6.95	-1.7	-0.8	0.05
GW	67	1	7.45	-3.15	-1.07	6.95	-3.15	-1.07	0.05
GW	68	1	7.45	-4.6	-1.33	6.95	-4.6	-1.33	0.05
GW	69	1	7.45	-5.25	0	6.95	-5.25	0	0.05
GW	70	1	7.45	-4.6	1.33	6.95	-4.6	1.33	0.05
GW	71	1	7.45	-3.15	1.07	6.95	-3.15	1.07	0.05
GW	72	1	7.45	-1.7	0.8	6.95	-1.7	0.8	0.05
GW	73	1	7.45	-0.88	0.8	6.95	-0.88	0.8	0.05
GW	74	1	7.45	-0.38	0.8	6.95	-0.38	0.8	0.05
GW	75	3	6.95	-0.88	0.8	6.25	-0.88	0.8	0.05
GW	76	3	6.95	-0.38	0.8	5.95	-0.38	0.8	0.05
GW	77	1	5.95	-0.38	0.8	5.95	-0.58	0.8	0.05
GW	78	1	5.95	-0.58	0.8	6.25	-0.88	0.8	0.05
GW	79	5	5.95	-0.38	0.8	4.2	-0.38	0.8	0.05
GW	80	5	5.95	-0.58	0.8	4.2	-0.58	0.8	0.025
GW	81	1	4.2	-0.38	0.8	4.2	-0.58	0.8	0.025
GW	82	3	4.2	-0.38	0.8	2.95	-0.38	0.8	0.025
GW	83	3	4.2	-0.58	0.8	2.95	-0.58	0.8	0.025
GW	84	91	1.49	16.65	1.94	1.49	-16.65	1.94	0.125
GW	85	91	3.35	16.65	4.36	3.35	-16.65	4.36	0.125
GW	86	91	5.21	16.65	6.77	5.21	-16.65	6.77	0.125
GW	87	91	7.07	16.65	9.19	7.07	-16.65	9.19	0.125
GW	88	91	9.81	16.65	12.75	9.81	-16.65	12.75	0.125
GW	89	91	12.55	16.65	16.32	12.55	-16.65	16.32	0.125
GW	90	91	15.29	16.65	19.87	15.29	-16.65	19.87	0.125
GW	91	91	1.49	16.65	-1.94	1.49	-16.65	-1.94	0.125
GW	92	91	3.35	16.65	-4.36	3.35	-16.65	-4.36	0.125
GW	93	91	5.21	16.65	-6.77	5.21	-16.65	-6.77	0.125
GW	94	91	7.07	16.65	-9.19	7.07	-16.65	-9.19	0.125
GW	95	91	9.81	16.65	-12.75	9.81	-16.65	-12.75	0.125
GW	96	91	12.55	16.65	-16.32	12.55	-16.65	-16.32	0.125
GW	97	91	15.29	16.65	-19.87	15.29	-16.65	-19.87	0.125
GW	98	15	13.7	3.5607	0	13.7	-3.5607	0	0.043575
GW	99	15	20.63465	3.5607	0	20.63465	-3.5607	0	0.043575
GW	100	15	27.5693	3.5607	0	27.5693	-3.5607	0	0.043575
GW	101	15	34.50395	3.5607	0	34.50395	-3.5607	0	0.043575
GW	102	15	41.4386	3.5607	0	41.4386	-3.5607	0	0.043575
GW	103	15	48.37325	3.5607	0	48.37325	-3.5607	0	0.043575
GW	104	15	55.3079	3.5607	0	55.3079	-3.5607	0	0.043575
GW	105	15	62.24255	3.5607	0	62.24255	-3.5607	0	0.043575
GW	106	15	69.1772	3.5607	0	69.1772	-3.5607	0	0.043575
GW	107	15	76.11185	3.5607	0	76.11185	-3.5607	0	0.043575
GW	108	15	83.0465	3.5607	0	83.0465	-3.5607	0	0.043575
GW	109	15	89.98115	3.5607	0	89.98115	-3.5607	0	0.043575
GW	110	15	96.9158	3.5607	0	96.9158	-3.5607	0	0.043575
GW	111	15	103.85045	3.5607	0	103.85045	-3.5607	0	0.043575
GW	112	15	14.198	3.5607	0	14.198	-3.5607	0	0.043575
GW	113	15	21.13265	3.5607	0	21.13265	-3.5607	0	0.043575
GW	114	15	28.0673	3.5607	0	28.0673	-3.5607	0	0.043575
GW	115	15	35.00195	3.5607	0	35.00195	-3.5607	0	0.043575
GW	116	15	41.9366	3.5607	0	41.9366	-3.5607	0	0.043575
GW	117	15	48.87125	3.5607	0	48.87125	-3.5607	0	0.043575
GW	118	15	55.8059	3.5607	0	55.8059	-3.5607	0	0.043575
GW	119	15	62.74055	3.5607	0	62.74055	-3.5607	0	0.043575
GW	120	15	69.6752	3.5607	0	69.6752	-3.5607	0	0.043575
GW	121	15	76.60985	3.5607	0	76.60985	-3.5607	0	0.043575
GW	122	15	83.5445	3.5607	0	83.5445	-3.5607	0	0.043575
GW	123	15	90.47915	3.5607	0	90.47915	-3.5607	0	0.043575
GW	124	15	97.4138	3.5607	0	97.4138	-3.5607	0	0.043575
GW	125	15	104.34845	3.5607	0	104.34845	-3.5607	0	0.043575
GW	126	7	7.2	-1.125	-0.8	7.2	1.125	-0.8	0.0216
GS	0	0	0.0254		' All in in.
GE	0
EK
LD	5	0	0	0	2.5e7	0
EX	0	126	4	0	1	0
GN	-1
FR	0	1	0	0	761	0
 
#3 ·
On the rescaled model above, each of the directors is 7.12 inches long (7 1/8" or 180.88 mm). They are .498 inches wide (1/2" or 12.65 mm) and .08716 inches thick (between 11 and 12 gauge or 1.11 mm), although anywhere from 1/16 to 1/8 inches thick should be fine.

The director spacings are measured as in the top view point diagram below. The center of the balun connection point is zero. The distance from it to the first directors (D1's) first edge is 6.5" (165.1 mm) as illustrated. So on for the rest of the directors.



The director measurements along the boom are:
Driven Element Balun Connection Point Center = 0"
D1 - 6.5" (165.1mm)
D2 - 13.43" (341.2mm)
D3 - 20.37" (517.3mm)
D4 - 27.30" (693.5mm)
D5 - 34.24" (869.6mm)
D6 - 41.17" (1045.8mm)
D7 - 48.11" (1221.9mm)
D8 - 55.04" (1398.0mm)
D9 - 61.98" (1574.2mm)
D10 - 68.91" (1750.3mm)
D11 - 75.85" (1926.5mm)
D12 - 82.78" (2102.6mm)
D13 - 89.72" (2278.7mm)
D14 - 96.65" (2454.9mm)


The length of the boom on the CM4248a / CM3023 increases by about a foot with the mod.

The possibility of using fat 1" diameter aluminum tube directors may also give another bit of additional low channel gain. That modeling will have to wait for another day, heh.
 
#10 ·
My mistake. I was misreading the drawing. My middle initial is C for confusion. Let me re ask my question. What would be the dipole length if it was modified for channel 20 and how would it affect the spacings? I'm assuming the dimension from dipole to first director would be all thats affected.Thanks.
 
#11 ·
What would be the dipole length if it was modified for channel 20 and how would it affect the spacings?
Right now, the dipoles natural low SWR is at channel 23, so enlarging it for channel 20 isnt going to do a lot.

Are you just going to shoot for channel 20 ? I did a test using fat 1" diameter directors instead of the flat ones, same length and spacings*, and the fat 1" diameter directors pushed the gain curve peak further to the left. That would boost channel 20 gain. Of course, you can then forget about channels in the 40's.

*Since the measurements above are to the front edge of the director, to find the center spacing for the 1" dia fat directors, add .5" to the above.
 
#12 ·
Thanks again. Your information will give me some fun experimenting with different size directors and still get channel 44.Other than that the next highest channel that I would be interested in would be 32. Now I'm going to ask a question that may need to be in a different thread.If so please tell me which thread so I can ask there. Are there any modifications that can be done to a 4228 old style to divert the frequency range to channels 18-44? I've seen discussions on modifying the new style 4228 but not the old. Thanks for putting up with me. Buy the way, what would be an affordable signal strength meter?
 
#13 ·
That is awesome, 300ohm. Thanks.

Do you have any idea how the 3023 with the typical directors would compare with the otherwise-identical older 4248 that has the diamond-shaped directors?

Anyway, this is probably already the best readily-available yagi out there for the lower UHF channels. Nice to see it modified to make it even better.
 
#14 ·
Do you have any idea how the 3023 with the typical directors would compare with the otherwise-identical older 4248 that has the diamond-shaped directors?
The ones with the diamond shaped directors were called CM4248/CM3023 also ??

Theres a couple of those around town here. :p

Someone would have to post the dimensions of those diamond shaped directors.

Id also love to get the dimensions of those models with the round disc reflectors.

Keep in mind, I think most of those funny shaped directors were developed by the marketing dept, since very few new designs use them. They just didnt seem to last but for one model run.

The best shape for a director, I feel, is governed by the shape of the driven element. So in the case of the CM4248/CM3023, it should be a solid, closed end "outie", bowtie.


Anyway, this is probably already the best readily-available yagi out there for the lower UHF channels. Nice to see it modified to make it even better.
The CM4248/CM3023 mod is pretty easy since the reflector and driven element are already geared for the lower channels.

Some other mods for other antennas is like trying to turn chicken shat into chicken salad, heh.
 
#16 ·
300ohm said:
Someone would have to post the dimensions of those diamond shaped directors.
I'll post the diamond-shaped ones if you're interested. I'd read somewhere basically what you said, that CM discontinued the diamond-shaped directors because they really didn't do any good, but I'd assume it would have *some* effect one way or another.

Id also love to get the dimensions of those models with the round disc reflectors.
Hmm, round disc reflectors? What are these?
 
#17 ·
ADTech just posted a link to A-D 91XG Technical Data Sheet in the A-D Thread:
http://www.antennasdirect.com/cmss_files/attachmentlibrary/91XG-TDS.pdf

Note that using THEIR dimensions, (patch?) model and a very pricey simulation program,
Gain Max was 18.28 dBi on 765 MHz, with 17.44 dBi on 698 MHz and 11.81 dBi on 470 MHz.

This is about 0.5 dB more on the high freqs and about 0.5 dB less on the low freqs
than Ken Nist's cm4221a.ez.nec results...using Ken's measurements & wire model....
this perhaps illustrates the inherent need to DON'T SWEAT THE DECIMALS:
http://photos.imageevent.com/holl_ands/yagis/91xg//A-D 91XG - UHF Gain and SWR.jpg
 
#18 ·
Hmm, round disc reflectors? What are these?
Heh, typo. I meant round uhf disc directors.

I believe it was CM or Winegard (but I could be wrong) in the early 80's, that had a stamped uhf lpda front end that used round disc directors. The 2 stamped uhf lpda sections were curled so they had a slightly rounded look too.


It looks like the CM corner reflector yagi with the diamond shaped directors was a model CM-4257.



http://www.digitalhome.ca/forum/showthread.php?t=41072&page=21
 
#20 ·
They look like hollow rods cut down the middle (looks U-shaped) and attached directly to the boom, no?
On the RS VU series, yes they are. But the round uhf disc directors Im referring to are solid stamped round discs, in the area of 4 to 6 inches in diameter.

Ive been searching thru google images and have yet to find a picture of those antennas, which is surprising because they were fairly common around here in the early 80's.
 
#21 ·
300, I'm pretty sure that 4257 was the longer version of the 4248... Notice how it looks like it has a longer boom, and the reinforcement double boom to boot. Boy would I love to have one of those! But the one I have is a 4248, I promise. :) I even still have the 8-foot long box (or whatever crazy length it is) the 4248 came in. I wonder if the "a" in the 4248a you mention is the later one with the more usual directors?

Actually, I thought I read somewhere (maybe on Nist's site?) that the 3023 had the different model name because it was made with a split boom for cheaper shipping. That super-long box I have would have to go freight and would cost a ton to ship. I got lucky enough to see on the local AVS forums for OTA that someone in my little city had found the 4248 at a local electronics wholesaler. I felt pretty stupid after having various antennas shipped in and driving 1.5 hours one-way to Frys that I never tried this local place about two miles from our office!

Anyway, I'm determined to take some pics with a ruler today after I was delinquent in taking some follow-ups of that Wade 1446 I have. :( Thinking of that, I bet the measurements on it are really close to the mods you posted for this one.
 
#23 ·
Okay, for anyone interested, here are the funky diamond shaped directors on my 4248. Probably just a marketing gimmick, but maybe interesting nonetheless.





 
#25 ·
here are the funky diamond shaped directors on my 4248.
OK, it looks like each half of the diamond shape director is 5.25" long by 2.375 inches high, with an air space between the halves of 2.5 inches.

Since theyre bent, I need to know how deep the pocket is on the director half (probably best to measure a few for depth and then take an average) and also how high is the middle flat section that isnt bent forward.

Then if you could, measure the distances from the corner reflectors apex to each of the directors rivet center.

This rivet on each.
 
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