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Author Topic: Diversity receiving antenna  (Read 2846 times)
KB0TXC
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Posts: 79




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« on: September 24, 2013, 04:46:56 AM »

Hi,

I am almost complete with the install of my 4BTV. Last thing to do is trench a slot for the conduit and coax, and finish the radials.

So, I was contemplating whilst listening to the QRMers on 40 last night, and my mind drifted diversity reception. What sort of receiving antenna array would be good for diversity reception so that I would not have to endure atmospheric fade whilst listening to the  highly intellectual conversation (or lack thereof) and strange sounds coming from the QRM sources?

In all seriousness, I have an elderly but very functional R-70 receiver and was thinking of getting another to experiment with diversity reception, and was wondering what sort of antenna set up would be good for this.

Best,

Joe KB0TXC
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K7KBN
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Posts: 2802




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« Reply #1 on: September 24, 2013, 12:12:31 PM »

My experiences with diversity reception suggest, in your case, a horizontal dipole or doublet at the same height.  Maybe other verticals around the area; this is a great case for experimenting.
You will want your antennas at least one wavelength apart.  That is the great thing about being stationed on an aircraft carrier:  you actually have ROOM to do things like this!
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73
Pat K7KBN
CWO4 USNR Ret.
KC4MOP
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Posts: 734




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« Reply #2 on: September 24, 2013, 06:01:08 PM »

A lot of space between antennas and 2 receivers for diversity. Something in between the receive outputs to select the best signal.
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K3GM
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Posts: 1799




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« Reply #3 on: September 24, 2013, 07:12:26 PM »

I've experimented with diversity receive on my dual receiver K3 on 10m FM to reduce the deep fade in the incoming signal as the polarization rotates around. I use a 3 element yagi on a tower, with a ground mounted vertical located about 3 wavelengths away.  On that band, the effect of the second antenna is remarkable with the signal staying pretty steady while I'm use to hearing nulls so deep that a signal can go from near full quieting to barely getting through, back to full quieting in a matter of seconds.
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K0ZN
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Posts: 1548




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« Reply #4 on: September 24, 2013, 08:23:56 PM »


When I was in the Army Signal Corps, we had some large (very large by ham standards) antenna systems that provided diversity reception. The military systems used both polarization and space diversity (there is also frequency diversity). It was fairly complex stuff with combiners, etc., but it does work to reduce QSB.  I have also "played" with simple manual switching between a good 40 m ground mounted vertical and a large horizontal antenna; no question, a lot of what we think of as fading is just polarization rotation and it seemed to me that 40 M was particularly susceptible to that. More often than not (assuming relatively decent band conditions) if you get a deep fade on one polarization, simply switching to the other one will bring the signal right back up. Problem is, this occurs pretty quickly and quite frequently in some conditions and doing the switching manually is almost impractical because you are just constantly flipping back and forth. Kind of depends on how much effort you want to put into it. My take was that during a QSO it was not really all that practical to keep switching between antennas unless the QSB was fairly slow...."your results may vary". Regardless, having two antennas with different polarization can be worthwhile/handy and they usually have different angles of radiation. Large TRUE longwire systems (antennas of many wave lengths) also reduce QSB significantly, but they require real estate well beyond reality for most hams.

73,  K0ZN
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KC4MOP
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Posts: 734




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« Reply #5 on: September 25, 2013, 03:46:36 AM »

I envy the guys who were actually working in HF comm centers in the military. We taught it at Ft Monmouth in 1968 but actually being deployed to 'Nam; the military graduated to tropospheric scatter for the long shots within country and VHF for the tactical comms. How communications left Viet Nam to get back to the USA was not clear to me. I know that I played music from a reel-to-reel into a tropo channel not being used and that was relayed all over Viet Nam and was patched into Germany somehow. AFVN radio would only play certain hits on the radio. No protest songs allowed! We would get calls to request music from a lot of strange places...Working "mids" we did crazy things.
I have personally noticed on 40M the characteristic fading and how different it can be between a vertical and my Yagi. Sometimes that constant deep fade and distortion heard on the vertical and switch to the Yagi and perfect reception.
The long pleasant fade we might remember was listening to skywave or "DX" on the AM radio band.
Fred
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W5WSS
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Posts: 1726




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« Reply #6 on: September 25, 2013, 07:32:16 AM »

Hello I did some diversity using two identical rectangular loops both identically vertically polarized and broadside relative to each other I was interested to try and see the relationship of phase shift and timing relative to the two antennas practically occupying the same space.

Even though the antennas were at the same height, presenting all of the same specifications and DE coupled as much as possible the two antennas positioned and held did respond equally to demonstrate that yes indeed the utility was actually valuable in serving to recover the equal signal strength during instant a/b switching so much so that total loss of signal on one antenna during a phase shift or fade was recouped by the other and sometime extremely like 20db or more a very usefull utility indeed.
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K0ZN
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Posts: 1548




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« Reply #7 on: September 25, 2013, 08:33:03 PM »

KC4MOP:

 "How communications left Viet Nam to get back to the USA was not clear to me."

 Two ways.... (1.) a small amount was via Large HF systems, one being at Long Binh using large Rhombics; HF was mostly encrypted RTTY circuits and some encrypted voice and (2.) Most of it went through the Vung Tau ICS site/Co. A, 369th Sig BN, which I was OIC at in '70-'71.  For obvious reasons, it was not publicized, as there was an undersea cable that came ashore and terminated at the Vung Tau ICS site and the multiplexed circuits were broken out and sent in and up country via high power Troposcatter systems. We had multi-channel tropo shots to Cam Ranh, Pleiku, DaNang, Nha Trang, Can Tho and Korat, Thailand. Closer places were by point-to-point microwave shots.  (Perspective: We had three 200KW generators to run the site.) A piece of trivia that will interest you as a ham. Our "last resort back up" was two Drake TR-4's into dipoles strung between the tropo arrays. We could patch into any of the non-secure stuff like AFVN, the AP News and other circuits which was really nice.... kept us in touch with the 'world'. We also had access to the AutoVon which allowed some phone calls home now and then, typically in the middle of the night when there were usually some unused circuits. It was a pretty interesting gig for a signal guy. Worst part was that we were pretty isolated up on that mountain top....good location for tropo but a little spooky at times. FYI.... the tropo systems had triple diversity: Polarization, Space and Frequency. We had chart recorders monitoring each receiver and it was interesting to watch how the various signals held and faded at different times.

73,  K0ZN
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