Occasionally, I get to go for a nice walk in a snowstorm. No, I am not being sarcastic. It is the middle of March and winter has decided to make an appearance. One of the FM stations we take care of went off the air and the remote control was not able to get the transmitter to come back on, so a stroll through the woods was necessary. This station is located at Sam’s Point Preserve, in Craigsmore NY.
Self-supporting tower has ATT and a Low Power TV station
The site is owned by Vertical Bridge. There are a few tenants on the tower and fortunately, somebody left the gate open before it snowed. I was somewhat dreading trying to wrestle with it when I got to the site.
The problem itself seems to be due to a power hit; the main transmitter was off and the remote control, a wheezing Genter VRC-2000, was not able to control either the main or the backup. Those should be replaced at some point.
Neighboring tower
There are several other towers up here for various cell carriers, 911 dispatch, etc.
My SO decided to come along.
My phone said we walked 2.7 miles round trip, which sounds about right. The station is back on the air. When I can get up there with a vehicle in a few weeks, I will look into the remote control problem.
Had to do some work at a transmitter site today and had to put the backup transmitter on the air for a few minutes.
WFLY backup transmitter, on the air
These were good units in their day and many continue on. This transmitter was new in 1986 and served as the main transmitter until 2015 or so. This unit still has the tube driver (4CX250B) which tended to use a set of tubes every year or so. The PA tube normally lasted 4 years or so.
Meters
I miss the analog meters sometimes. There is something satisfying watching all the meters come up together when the plate on button is pushed.
UPDATE and bump: This post is from eleven years ago, but I have been working on an SDR project using one of the RTL- 2832 chips. I had to make two more of these units, so the prices and part numbers have been updated.
I have acquired one of those broad-banded software-defined radios, an Icom PCR-1000 to be precise, and all is well. I am enjoying listening to various MF, HF and VHF radio stations. However, there is a slight problem. Very slight, almost too small to even mention, more of an inconvenience than a problem. Still, if I am being inconvenienced, then others are too. This issue is with the antennas. My K9AY antenna works wonderfully from 500 KHz to 25 MHz or so. My discone antenna works wonderfully from about 30 MHz all the way up to about 1 GHz. In order to enjoy the full range of the receiver, I need to switch antennas. I have a small switch on my desktop, but it seems inconvenient to reach over and switch it when going from the AM band to the FM band or something similar. Therefore, I have decided that I need an HF/VHF receiver diplexer. One would think that such hardware is ready-made for such instances. However, nothing I could find commercially would do the trick.
Thus, since I could not buy one, I decided to build one to add to my collection of receiver doo-dads and nick knacks. The design is relatively easy, a back-to-back low pass/high pass filter system with a 50-ohm impedance throughout. Something with a sharp cut-off around 30 MHz or so:
Diplexor plot
Looks pretty good, 5th order Chebyshev filter, perhaps .1 dB ripple in the pass bands if well made. Schematically:
HF VHF diplexor schematic diagram
Then it comes down to the building. Since this is going to be used in the UHF range, care and attention needs to be paid to the layout of the components and the design of the circuit board. Some of those capacitance values are not standard, however, by using two capacitors in parallel, one can get pretty close. Since this is going to be used for receiving only, I may be splitting hairs, however, I have found that well-designed and built equipment is worth the extra effort.
The board layout looks like this:
HF VHF receiver diplexer board
I tried to keep the traces as close to 50 Ohm impedance as possible.
As one may be able to discern, C2 and C3 are in parallel to make 192 PF, C5 and C6 are in parallel to make 60 PF, and C7 and C8 are in parallel to make 163 PF.
The input and output RF connectors are whatever the builder wants to use, however, I would recommend at least BNC or type N for the VHF/UHF side. My unit has all type BNC female connectors. Parts list:
Nomenclature
Value
Mouser number
Cost (USD)
C1
150 PF SMT
581-12065A151FAT2A
0.72
C2
12 PF SMT
581-12061A120JAT2A
0.26
C3
180 PF SMT
810-CGA5C4C0G2J181J
0.27
C4
68 PF SMT
77-VJ1206A680FXACBC
0.59
C5
50 PF SMT
581-12062A500KAT2A
0.41
C6
10 PF SMT
80-C1206C100J2G
0.54
C7
3 PF SMT
581-12061A3R0CAT2A
0.34
C8
160 PF SMT
581-12065A161J
0.34
Case
Diecast, 4.3 x 2.3”
546-1590WB
10.71
I chose a smallish, diecast aluminum case, which matches my other receiver gear. The circuit board noted above is 2.9 x 1.7 inches, which is a little bit small. I used 18 gauge wire between the input/output connectors and the board.
The inductors were made by hand. I used a small screwdriver as a winding form, making the turns tightly and then spreading them out to the proper distance.
Inductor chart:
Inductor
Value (nH)
Diameter (mm)
Turns
Length (mm)
L1
173
8
6
9.5
L2
468
8
10
9.8
L3
414
8
9
8.7
L4
146
8
5
7.2
L5
186
8
6
8.6
The most expensive part was the circuit board, which cost about $16.00. The rest parts were about $22.00 including shipping.
As built photos:
HF VHF diplexer with components installed
HF VHF diplexer input side
HF VHF diplexer completed.
I have installed this already and it works great. I will need to get the spectrum analyzer out and run some signals through the various ports to see the attenuation and 3 dB roll-off points.
By now, most have heard of the passing of Ray Topp, publisher of Radio Guide magazine. I was shocked when I first learned about it in the middle of February. The family has decided to cease publishing the magazine, which is understandable, but also a loss for the industry. The goal of Radio Guide was to provide “real-world technical information.” When I wrote an article, I always thought about the various people I worked with over the years and what they were concerned with.
The last I heard from Ray was the third week in December. He said he had a bout of COVID and there were some complications. He said he was trying very hard to get the January/February 2023 issue done. I sent in my article in early January but never heard anything back, which is unusual. When the publishing date came and went, I thought that perhaps he was still recovering. Unfortunately, that was not so.
My final article for Radio Guide was to be titled: Learning with the Libra VNA
